Anionic and zwitterionic copper(i) complexes incorporating an anionic N-heterocyclic carbene decorated with a malonate backbone: synthesis, structure and catalytic applications

Abstract

The anionic malonate-derived N-heterocyclic carbenes (maloNHCs) react cleanly and rapidly with copper chloride to generate the anionic complexes of type [(maloNHC)CuCl]·Li, which crystallize in the solid state either in an oligomeric trimer arrangement or in polymeric helixes depending on the substitution pattern and the solvent. Ten zwitterionic heteroleptic Cu(I) complexes combining the anionic maloNHC and a neutral imidazol-2-ylidene are also obtained in a very selective manner and fully characterized. Whereas the anionic complexes are relatively active catalysts for the hydrosilylation of carbonyl compounds, the zwitterionic complexes reveal to be efficient and extremely robust pre-catalysts for the intramolecular cyclopropanation reaction of a diazo ester and outperform the corresponding cationic Cu(i) complexes with classical imidazol-2-ylidenes.

Mercury(II) Complexes of Anionic N-Heterocyclic Carbene Ligands: Steric Effects of the Backbone Substituent

“…The anionic, six-membered N-heterocyclic carbene ligand precursor 1a has been reported earlier [32]. The anionic-NHC ligand precursors 1a and 2a were synthesized using the strategy reported by César et al (from the condensation of N,N'-bis (2,6-diisopropylphenyl)formamidine and monosubstituted malonic acid) [30].…”

“…Reactions of these anionic NHCs with transition metals afford corresponding zwitterionic complexes. Anionic, six-membered ring NHCs based on a malonate unit (maloNHC), introduced by Cesar, Lavigne and co-workers [30], are particularly interesting as they are attractive ligands to stabilize late transition metal ion complexes such as those involving Ag I , Au I , Rh I , Cu I [30][31][32][33][34][35], as well as Fe II [36].…”

Zwitterionic Mixed‐Carbene Coinage Metal Complexes: Synthesis, Structures, and Photophysical Studies

“…The precursor ( malo NHC)H was synthesized according to a literature procedure . The corresponding anionic carbene can be generated in situ or isolated in an intermediate step in the presence of a strong base [KN(SiMe 3 ) 2 or n BuLi].…”

“…CH 2 Cl 2 , diethyl ether, THF, and hexane were freshly distilled from appropriate drying agents. ( malo NHC)H, the corresponding carbene ( malo NHC)Li, ( Et2 CAAC)CuCl, ( Et2 CAAC)AgCl and ( Et2 CAAC)AuCl were synthesised according to literature procedures. The identity and purity (≥95 %) of the compounds were established using elemental analyses, multinuclear NMR spectroscopy and X‐ray diffraction analysis.…”

“…This family of ligands has been intensively studied, and some of them were used to stabilise group 11 metal ions . Anionic 6‐ring NHC ligands based on a malonate unit ( malo NHC ) , have also been developed and coordinated to silver and to gold halide and phosphane complexes, including reports on copper halide and copper bis(carbene) complexes . To the best of our knowledge, anionic carbene ligands have not been used in the context of photoluminescence studies .…”